Technical Abstract:
An immobilized lipase packed-bed bioreactor was developed for esterifying the free fatty acids in greases as a pretreatment step in the production of their simple alkyl esters for use as biodiesel. The immobilized lipases used in the study were immobilized preparations of Candida antarctica (C. a.), and Thermomyces lanuguinosa (T. l.). Enzymatic pre-esterification was carried out in a solvent-free recirculating packed-bed column reactor using the immobilized lipase as the stationary phase and methanol and restaurant grease of varying FFA content (8-36%) as substrates. The reactor was operated at 50°C using varying mole ratios of reactants (FFA in the grease to alcohol) to maximize FFA esterification. In general, the conversion of FFA to methyl esters increased linearly with time but reached a steady state condition after 3 hours. Under optimum operating conditions (flow rate 10 mL per min, temperature 50°C, alcohol to grease FFA mole ratio 1.0:1.1), the remaining % FFA was < 1.5% the original amount after 1 hour. The biocatalyst could be reused with only minimal loss of its initial esterification activity. The data indicate that the bioreactor could be used for either pretreatment of the grease (esterifying the free fatty acid) or full production of biodiesel from the grease.